An accurate mass spectrometry methods for determining of properties of gas phase samples are in very important role e.g. in atmospheric studies, such as studying e.g. roles of different chemical substances, such as ammonia, amines, in atmospheric nanoparticle formation. Especially there is a need for better knowing or determination of low concentrations and variability of atmospheric ammonia and amines and highly oxidized organics, as an example. In addition very accurate methods for determining of properties of gas phase samples, such as amines, are needed also in other fields, such as in a medical industry and diagnostics, security and food processing industry.
However, measurement of trace amounts of gaseous compounds for example from air is extremely difficult, as their concentration is minimal compared to the total air molecule concentration, and due to the large variety of the different gases compounds and their isotopes. However, some of these molecules have a significant effect on the air chemistry and aerosol formation, even in small amounts. Therefore exact measurements are needed for instance in atmospheric aerosol research.
Very often gas phase samples are analysed by a mass spectrometer, but also other detecting devices can be used, such as IMS-device (Ion Mobility Spectrometry) or DMA-device (Differential Mobility Analyzers). The mass spectrometer is detecting the mass to charge ratio of an ion or ion cluster, whereas IMS and DMA devices are based on the electrical mobility of the sample particles. As majority of sample particles, such as airborne molecules and clusters are initially neutral, they need to be charged before a measurement.
One exemplary method to charge the sample particles, such as ammonia or amine molecules and clusters, before the measurement and thereby provide an ion flow of sample constituents is chemical ionizing (CI) of the sample constituents using an ionizer.
There are, however, some drawback related to known solutions namely particles to be determined may stick to inner wall structures of the ionizer and afterwards be released back to the sample gas flow and induce signal in a detector. Thus it is said that the wall structures of the ionizer has a memory effect (or wall effect). Anyway this is a very undesired feature because the particles are released very randomly and thus they will disturb the measurement at first by sticking into the structure and thereby reducing a signal to be measured, and secondly by releasing to the later sample flow and increasing the signal of the later sample flow to be detected.